Place chicken breasts into a gallon Ziploc bag. (you can cut the chicken against the grain into strips if you'd like or wait until it's cooked before slicing) Set aside.
Mix together all marinade ingredients until sugar is dissolved.
Pour marinade over chicken, reserving 1-2 tablespoons to cook the peppers in if desired
Refrigerate for 2-3 hours (no longer than that)
When ready to cook remove chicken from marinade, pat chicken dry and let come to room temperature.
Add a tablespoon of oil to a cast iron skillet and heat over medium heat.
When the pan is hot, add chicken in a single layer.
When one side is browned, flip the chicken and continue cooking until done and slightly charred.
Remove chicken from pan and cover with tented foil to keep warm.
Add a little more oil to the pan if needed and the reserved marinade if using.
Add in peppers and onions and toss to coat.
Cook just until peppers become tender with a slight bite.
Add in the cooked chicken and toss.
Remove from heat.
Garnish with a splash of lime and fresh cilantro
Serve sizzling hot with flour tortillas and topped with sour cream, fresh pico de gallo and sliced avocado.